In our U.S. patent application Ser. No. 862,936, now U.S. Pat. No. 4,716,938, issued Jan. 5, 1988, we have disclosed a plug coupling of the type defined above constituting a pressure-tight plug coupling for a connecting means provided with a male or female threading. In a cylindrical housing a piston is shiftably mounted. A plurality of clamping jaws engages a front portion of the piston in a concentric arrangement about a longitudinal axis of the housing, the free ends of the clamping jaws being radially displaceable by means of a ramp arrangement during movement of the piston in an outward direction of the longitudinal axis relative to the housing, a pressure being applied against the rear end of the piston in order to move the clamping jaws in either of a connected and a disconnected position. In the absence of pressure, the piston is pulled into the interior of the housing by means of a compression spring arranged between the interior of the housing and the rear end of the piston. With one type of known plug coupling for a male threading connection, the piston is guided on a core, provided at its front end portion with a sealing element, shiftable in the axial direction by a limited distance and sealingly engaging an end surface of the male threaded connector upon application of the plug coupling. Fluid to be supplied through the connector is supplied through a laterally attached inlet port into the cylindrical housing and from there through the hollow core to the connection. The means applying pressure to the piston is formed either as a handle acting through a stud onto the rear end face of the piston or as a pressure fluid source exerting a corresponding pressure to the rear end face of the piston.
The forced back and forth axial movement of the piston may alternatively be accomplished by applying air under-pressure either to the rear end of the piston or to a piston surface forming part of a front pressure chamber. Such an alternative application of pressure is accomplished by shifting a sleeve arranged on the peripheral surface of the housing in the axial direction.
The known device has a stable construction and is easy to handle, in particular when a handle is used for activation. However, there are various applications where the size of the coupling is too large and the passage of the fluid is limited. Also, the costs of manufacture are only justified for operation at very high pressures.